Abstract
The mechanical stretching behavior of the poly(styrene-b-ethylene-co-butylene-b-styrene) (SEBS) triblock copolymer (87 wt% polyethylene-co-butylene (PEB), 13 wt% polystyrene (PS)) was investigated under three different stretching modes and through in situ small-angle X-ray scattering (SAXS) analysis. The strain energy density function was investigated based on the stress and stretching ratio (λ) relationship under uniaxial, planar extension, and equi-biaxial stretching modes. As a result, the cross-effect of strain represented by the second invariants of the deformation tensor (I2) was identified, and only the Ogden model found to fit the data. In the cyclic stretching tests, SEBS exhibited smaller hysteresis during cyclic equi-biaxial stretching compared to uniaxial stretching. In other words, the Mullins effect was found to be more obvious for uniaxial stretching than equi-biaxial stretching. The λ and the stretching ratio obtained from the crystal planes by SAXS (λSAXS) were compared to investigate the relationship between the change in the microdomain structure and the macroscopic mechanical properties. Thus, affine deformation was found to occur in the smaller λ region for both uniaxial and equi-biaxial stretching and deviation from affine deformation occurred for uniaxial stretching in the larger λ region. This is because the entangled loops of PEB chains serve as cross-linking points when the films are stretched under equi-biaxial stretching.
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Acknowledgements
This work was supported by the Impulsing Paradigm Change through Disruptive Technology (ImPACT) Program, JST CREST Grant Number JPMJCR17J4, and JST-Mirai Program Grant Number JPMJMI18A2, Japan. Synchrotron radiation X-ray scattering measurements were performed at BL40XU and BL05XU in the SPring-8 facility with the approval of the Japan Synchrotron Radiation Research Institute (JASRI; Proposal No. 2018B1035, 2019A1015, 2019B1011, 2020A1007). ND thanks Weeradet Sittiphon for his support with the mathematical calculation. Financial support for ND was provided by the International Graduate Course on Chemistry for Molecular Systems, Ministry of Education, Culture, Sports, Science and Technology (MEXT), Japan.
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Dechnarong, N., Kamitani, K., Cheng, CH. et al. Microdomain structure change and macroscopic mechanical response of styrenic triblock copolymer under cyclic uniaxial and biaxial stretching modes. Polym J 53, 703–712 (2021). https://doi.org/10.1038/s41428-021-00469-z
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DOI: https://doi.org/10.1038/s41428-021-00469-z
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